Elementi strutturali in calcestruzzo armati con barre in GFRP

Sono riportati alcuni risultati sperimentali, ottenuti dagli autori, riguardanti: - caratterizzazione meccanica a trazione di barre GFRP, anche di elevato diametro; - valutazione dell’aderenza tra barre in GFRP e calcestruzzo; - vita a fatica di solette da ponte rinforzati con barre in GFRP; - comportamento statico di elementi in calcestruzzo rinforzati con barre in GFRP soggetti ad elevate variazioni di temperatura

Progressive damage in stitched composites: Static tensile tests and tension-tension fatigue

The paper describes progressive damage in static tensile tests and tension-tension fatigue in structurally stitched carbon/epoxy NCF composites, in comparison with their non-stitched counterparts. Analogies between damage development in quasi-static tension and tension-tension fatigue are analyzed and links between the damage initiation thresholds in quasi-static tests and fatigue life are established

Liquid hot isostatic pressing of QE22A magnesium alloy: a preliminary test

A preliminary experimental comparison of the behaviour of aluminium and magnesium alloys subjected to Liquid Hot Isostatic Pressing (LHIP) is proposed. The two metals melt at approximately the same temperature.However, as a consequence of a larger deformability of magnesium at elevated temperatures, the choice of LHIP parameters – and especially the temperature at which the pressure is applied – in the present exploratory case was constrained to values far smaller than those one would like to select in order to improve the ultimate tensile stress and the elongation to fracture

tetraxial textiles assessment of mesoscale mechanical modelling by experimental measurements

Tetraxial technical textiles were recently manufactured by a new loom developed to weave yarns in four directions. The textile has warp, weft, and two diagonal yarns oriented at symmetrical angles (typically ±45°) with respect to the warp direction. The peculiar yarns distribution could enhance the mechanical response of the textile in multiple directions aiming to almost isotropic in-plane behaviour. For the prediction of the mechanical performance of such tetraxial textiles, a reliable and accurate predictive model is of relevant importance. The present investigation aims to adopt the finite element numerical approach at the mesoscopic scale to predict the mechanical response for any in-plane loading of tetraxial textiles. An accurate modelling of the constitutive behaviour of the fibrous yarns was adopted considering a hyperelastic model. The modelling of the tetraxial unit cell allowed to have the mechanical behaviour for uniaxial and biaxial tensile and for shear loading conditions. The assessment of the accuracy of the numerical model was performed considering a huge experimental campaign dedicated to several hybrid tetraxial textiles. The comparison highlights the accuracy of the numerical model to predict the nonlinear behavior of the fabric for any loading condition and to provide the proper mechanical model for further optimization of tetraxial textiles supposed for different industrial applications

Multi-instrument multi-scale experimental damage mechanics for fibre reinforced composites

© Published under licence by IOP Publishing Ltd. Reliable investigation of damage in fibre reinforced composites requires concurrent in- and ex-situ application of multiple instruments at different scale: digital image correlation, acoustic emission registration, optical/electron microscopy, C-scan, X-ray imaging and micro-computed tomography. The multi-instrument experimental mechanics allows detailed damage monitoring and inspection

Operating organic light-emitting diodes imaged by super-resolution spectroscopy

Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible. With the example of organic light-emitting diodes (OLEDs), spectral imaging with pixel-by-pixel wavelength discrimination allows us to resolve local-chain environment encoded in the spectral response of the semi-conducting polymer, and correlate chain packing with local electroluminescence by using externally applied current as the excitation source. We observe nanoscopic defects that would be unresolvable by traditional microscopy. They are revealed in electroluminescence maps in operating OLEDs with 50 nm spatial resolution. We find that brightest emission comes from regions with more densely packed chains. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating. This points the way towards real-time analysis of materials design principles in devices as they actually operateope

Investigating Bacterial Sources of Toxicity as an Environmental Contributor to Dopaminergic Neurodegeneration

Parkinson disease (PD) involves progressive neurodegeneration, including loss of dopamine (DA) neurons from the substantia nigra. Select genes associated with rare familial forms of PD function in cellular pathways, such as the ubiquitin-proteasome system (UPS), involved in protein degradation. The misfolding and accumulation of proteins, such as α-synuclein, into inclusions termed Lewy Bodies represents a clinical hallmark of PD. Given the predominance of sporadic PD among patient populations, environmental toxins may induce the disease, although their nature is largely unknown. Thus, an unmet challenge surrounds the discovery of causal or contributory neurotoxic factors that could account for the prevalence of sporadic PD. Bacteria within the order Actinomycetales are renowned for their robust production of secondary metabolites and might represent unidentified sources of environmental exposures. Among these, the aerobic genera, Streptomyces, produce natural proteasome inhibitors that block protein degradation and may potentially damage DA neurons. Here we demonstrate that a metabolite produced by a common soil bacterium, S. venezuelae, caused DA neurodegeneration in the nematode, Caenorhabditis elegans, which increased as animals aged. This metabolite, which disrupts UPS function, caused gradual degeneration of all neuronal classes examined, however DA neurons were particularly vulnerable to exposure. The presence of DA exacerbated toxicity because neurodegeneration was attenuated in mutant nematodes depleted for tyrosine hydroxylase (TH), the rate-limiting enzyme in DA production. Strikingly, this factor caused dose-dependent death of human SH-SY5Y neuroblastoma cells, a dopaminergic line. Efforts to purify the toxic activity revealed that it is a highly stable, lipophilic, and chemically unique small molecule. Evidence of a robust neurotoxic factor that selectively impacts neuronal survival in a progressive yet moderate manner is consistent with the etiology of age-associated neurodegenerative diseases. Collectively, these data suggest the potential for exposures to the metabolites of specific common soil bacteria to possibly represent a contributory environmental component to PD

Dysregulation of the Norepinephrine Transporter Sustains Cortical Hypodopaminergia and Schizophrenia-Like Behaviors in Neuronal Rictor Null Mice

A novel animal model highlights the link between Akt dysfunction, reduced cortical dopamine function, norepinephrine transporters, and schizophrenia-like behaviors